This invention relates generally to motors or actuators through which electrical energy is converted into mechanical energy by magnetostriction.
Linear motors based on electrostriction operating principles are well known and are similar in operation to magnetostrictive types of linear motors. In a magnetostrictive linear motor, an active element is movable in one direction of motion relative to a container associated with its stator. The movable element is tightly held in the container while the motor is deenergized. The stator also has already associated therewith an electromagnetically energized coil for generating a magnetic field that is oriented in the direction of motion imparted to the movable element. In continuous motion types of motors, having relatively small strokes, the movable element is maintained clamped to its stator at one axial location in the direction of motion. In motors producing discontinuous motion, the movable element is either clamped to the stator at two or more axial locations or the clamping location is changed during operation.
The use of polycrystalline Terfenol-D as a most desirable magnetostriction material has already been proposed for the movable element of magnetostrictive linear motors. Such active element material is magnetostrictively elongated by a localized magnetic field swept along the direction of motion as the element shrinks from the inner wall surface of its stator support lube by contracting uniformly in directions transverse to its motion. The movable element clamped to the stator support tube in the static condition of such motors is under randomly applied radial stress in multi-axis directions.
Various problems are inherent in the latter type of linear motor already known in the art. First, the polycrystalline Terfenol-D material must be ground into a near perfect circular cross-section in order to establish a uniform tight fit within the support tube. Second, any wear between the outer cylindrical surface of the movable element and the inner wall surface of the support tube renders the motor inoperative. Thirdly, motor performance is limited by its pre-stressed condition.
It is therefore an important object of the present invention to provide a linear motor of the type having the desirable properties of a crystalline Terfenol-D magnetostrictive element, but avoids the aforementioned problems associated therewith and meets the high levels of performance necessary for high power micropositioners, injection valves, micrometering valves and other devices relying on accurate linear motion.